This invention relates to urokinase inhibitors.
Urokinase (urinary-type plasminogen activator or uPA; International Union of Biochemistry classification number: EC 3.4.21.31) is a proteolytic enzyme which is highly specific for a single peptide bond in plasminogen. Cleavage of this bond by urokinase ("plasminogen activation") results in formation of the potent general protease plasmin. Many cell types use urokinase as a key initiator of plasmin-mediated proteolytic degradation or modification of extracellular support structures such as extracellular matrix (ECM) and basement membrane (BM). Cells exist, move, and interact with each other in tissues and organs within the physical framework provided by ECM and BM. Movement of cells within ECM or across BM requires local proteolytic degradation or modification of these structures, allowing cells to "invade" into adjacent areas which were previously unavailable to the cells.
Cellular invasiveness intiated by urokinase is central to a wide variety of normal and disease-state physiological processes (reviewed in: Blasi, F., Vassalli, J. D., and Dan, K. J. Cell Biol. 104:801-804, 1987; Dan, K., Andreasen, P. A., Grndahl-Hansen, J., Kristensen, P., Nielsen, L. S., and Skriver, L. Adv. Cancer Res. 44:139-266, 1985; Littlefield, B. A. Ann. N. Y. Acad. Sci. 622:167-175, 1991; Saksela, O. Biochim. Biophys. Acta 823:35-65, 1985; Testa, J. E. and Quigley, J. P. Cancer Metast. Rev. 9:353-367, 1990). Such processes include, but are not limited to, angiogenesis (neovascularization), bone restructuring, embryo implantation in the uterus, infiltration of immune cells into inflammatory sites, ovulation, spermatogenesis, tissue remodelling during wound repair and organ differentiation, fibrosis, local invasion of tumors into adjacent areas, metastatic spread of tumor cells from primary to secondary sites, and tissue destruction in arthritis. Inhibitors of urokinase therefore have mechanism-based anti-angiogenic, anti-arthritic, anti-inflammatory, anti-invasive, anti-metastatic, anti-osteoporotic, anti-retinopathic (for angiogenesis-dependent retinopathies), contraceptive, and tumoristatic activities.
Beneficial effects of urokinase inhibitors have been reported using anti-urokinase monoclonal antibodies and certain other known urokinase inhibitors. For instance, anti-urokinase monoclonal antibodies have been reported to block tumor cell invasiveness in vitro (Hollas, W., Blasi, F. and Boyd, D. Cancer Res. 51:3690-3695, 1991; Meissauer, A., Kramer, M. D., Hofmann, M., Erkell, L. J., Jacob, E., Schirrmacher, V. and Brunner, G. Exp. Cell Res. 192:453-459, 1991), tumor metastasis and invasion in vivo (Ossowski, L. J. Cell Biol. 107:2437-2445, 1988; Ossowski, L., Russo-Payne, H. and Wilson, E. L. Cancer Res. 51:274-81, 1991), and angiogenesis in vivo (Jerdan, J. A., Gilliam, K., Ransey, C. and Glaser, B. J. Cell Biol. 115[3 Pt 2]:402a, 1991). In addition, amiloride, a known urokinase inhibitor of only moderate potency, has been reported to inhibit tumor metastasis in vivo (Kellen, J. A., Mirakian, A. and Kolin, A. Anticancer Res. 8:1373-1376, 1988) and angiogenesis/capillary network formation in vitro (Alliegro, M. A., Alliegro, M. C. and Glaser, B. M. J. Cell Biol. 115[3 Pt 2]:402a, 1991).
Central to the ability of urokinase to mediate cellular invasiveness is the existence of specific high affinity urokinase receptors which concentrate urokinase on the cell surface, leading to the generation of locally high plasmin concentrations between cells and ECM or BM (Blasi, F., Vassalli, J.-D., and Dan, K. J. Cell Biol. 104:801-804, 1987; Roldan, A. L., Cubellis, M. V., Masucci, M. T., Behrendt, N., Lund, L. R., Dan, K., Appella, E., and Blasi, F. EMBO J. 9:467-74, 1990). High plasmin concentrations between invasive cells and ECM or BM are necessary in order to overcome inhibitory effects of ubiquitous plasmin inhibitors, such as .alpha..sub.2 -antiplasmin and .alpha..sub.2 -macroglobulin. Thus, it is cell surface receptor-bound urokinase, and not simply free urokinase secreted by cells, which plays the predominant role in initiating cellular invasiveness.